What is MHE?
Multiple Hereditary Exostoses (MHE), also called Hereditary Multiple Osteochondromas (HMO) or Multiple Osteochondromas (MO), is a rare genetic condition in which multiple benign bone growths, called osteochondromas, develop near growth plates of bones. Impacted areas can include arms, legs, fingers, ribs, pelvis, ankles, feet, scapula and spine.
MHE affects about 1 in 50,000 people. It follows an autosomal dominant inheritance pattern, meaning a single altered copy of the gene can cause the condition. Growths usually appear in childhood.
How Does MHE Affect the Body?
People with MHE often have growths on long bones, like the arms and legs, but they can appear anywhere on the skeleton. Osteochondromas very rarely grow on the face or skull. The growths can vary in size and shape. For some people they do not cause problems, while for others they can lead to pain, reduced movement, or challenges with alignment and how bones grow.
The severity of MHE can vary widely (even within families), with some people having only a few osteochondromas and mild symptoms, while others may develop many bumps that can cause significant challenges and physical limitations.
What Causes MHE?
MHE is primarily caused by mutations in the EXT1 or EXT2 genes. These genes play an important role in the production of heparan sulfate, a molecule that regulates cell growth and differentiation, especially in cartilage. Mutations in either of EXT 1 or EXT2 genes disrupt the normal functioning of cartilage cells, leading to abnormal bone growth and the development of multiple osteochondromas at the growth plates.
MHE is autosomal dominant, which means it only requires one copy of the mutated gene to inherit MHE. This is why some families have many people with MHE.
Sometimes MHE is caused by a spontaneous genetic mutation and only one person in the family has MHE. This person can pass MHE onto their children.
Types of Osteochondromas
Osteochondromas are classified based on their shape into two types: pedunculated and sessile.
Pedunculated Osteochondroma are connected to the bone by a narrow, stalk-like structure, resembling a mushroom.
Sessile Osteochondroma have a broad, flat base that merges more directly into the bone, without a distinct stalk. Sessile osteochondromas tend to appear as wide-based elevations of the bone surface and, while they protrude less than pedunculated osteochondromas, they can still cause discomfort or deformities as they grow.
How is MHE Diagnosed?
Doctors, most often Orthopedic Surgeons, diagnose MHE through a combination of medical history, physical exams, and imaging tests like X-rays. These tests help doctors see the growths to understand how they might be affecting bones and joints.
It can be helpful to confirm the diagnosis with genetic testing.
Information provided on MHELS.org is for educational and informational purposes only and is not intended to replace professional medical advice, diagnosis, or treatment. Always consult your healthcare team for decisions regarding your care.
